The plant is proposed for 50 acres on Applebutter Road near Bethlehem's border with Lower Saucon Township and will feed power to the mid-Atlantic region power grid that includes Delaware, New Jersey, Maryland, Virginia, the District of Columbia and most of Pennsylvania.

Approval comes after a November hearing at which a half-dozen residents expressed concern about emissions from the plant.

In response to those concerns and taking into account a mountain of technical testimony, Carmon said the DEP imposed lower emission rates and reduced operating hours during peak operating conditions than the company had wanted.

But Roberta Brown, vice president of business development for Conectiv, said the restrictions don't pose a problem to the company's plans to have some of the generators up and running by the end of the year.

"We are starting construction immediately," Brown said. "We anticipate this unit is going to run only 40 to 60 percent of the time. We didn't expect to be running 24 hours a day, 365 days a year."

The plant is designed for operation primarily during peak demands on the power grid and is triggered into operation when electricity prices are at their highest.

Carmon said the plant will face restrictions even during the peak demand times between Memorial Day and Labor Day, when ozone in the atmosphere is typically at its worst. "They're going to have to make both environmental and economic judgments about when to put the plant into peak operation," Carmon said. "They're going to have to balance the amount of hours they operate in peak power."

Up to certain limits, the company will be permitted to run when there is emergency demand for electricity, according to Carmon.

Once the facility is built, Conectiv will be required to install continuous emission monitors and DEP will require additional testing before an operating permit is issued.

With all other local approvals and permits in hand, the gas-to-electric facility is expected to surge onto the regional power grid as soon as fall, but tax revenues to the city, Lower Saucon Township, Bethlehem Area School District and county will take a little longer to arrive.

The plant is in a tax abatement district, so the levy will rise at 10 percent per year over 10 years until the company is paying the full rate.

It's unclear what assessed value the plant will have for tax purposes, but a $600 million market value would bring the city $3.3 million a year when it reaches the full rate.

Whatever amount of tax revenue flows from the project, Bethlehem Mayor Don Cunningham said it will be a boost to the city's threadbare budget. "There is a wide range of opinions about whether it's going to be a large or small amount but what is clear is that it will bring us revenues and makes good use of unproductive industrial land," Cunningham said.